64 MECHANICS. 



not the case ; nearly the whole of it rests upon the ful- 

 crum. We often see proofs of this error in common 

 practice, where fulcrums or props entirely insufficient 

 to uphold the enormous weight to be raised are at- 

 tempted to be used. If the weight, for instance, be 

 ten times as near the fulcrum as to the power, then 

 nine tenths of the weight rests upon the fulcrum, and 

 the remaining tenth only is sustained by the lifting 

 power. The lever only allows the power to expend it- 

 self through a longer distance, and thus, by concentra- 

 ting itself at the weight, to elevate the latter through 

 the shorter distance, according to the rule of virtual 

 velocities already explained. 



The fulcrum may be placed between the weight and 

 Fig. 42. the power, as in 



__^^ Fig. 42, or the 



Lever of the first kind. placed between 



Fig. 43. the fulcrum and the 



// L weight, as in Fig: 



^ - ^ - 48, the same princi- 



Lever of the third kind. ^^Q of virtual Veloci- 



ties applying in all cases. 



Where the fulcrum is between the power and the 

 weight, as in Fig. 42, it is called a lever of the first 

 kind. 



Where the weight is between the fulcrum and the 

 power, as in Fig. 41, it constitutes a lever of the 

 seco7id kind. 



Where the power is between the fulcrum and the 

 weight, as in Fig. 43, it is termed a lever of the third 

 kind. 



